Methods for preparing single phase molten baths of alkalinous chlorides, titanium chlorides, and alkalinous metals



Aug. 25, 1959 w. w. GULLETT 2, METHODS FOR PREPARING SINGLE PHASE MOLTENBATHS OF ALKALINOUS CHLORIDES, TITANIUM CHLORIDES AND ALKALINOUS METALSFiled May '20, 1957 if: y ,0 O a J;

MOLTEN ELECTROLYTE wamww 2w INVENTOR United States Patent METHODS FORPREPARING SINGLE PHASE MOLTEN BATHS 0F ALKALINOUS CHLO- RIDES, TITANIUMCHLORIDES, AND AL- KALINOUS METALS William W. Gullett, College Park,Md., assignor to Chicago Development Corporation, Riverdale, Mat, acorporation of Delaware Application May 20, 1957, Serial No. 660,418

1 Claim. (Cl. 20464) This invention relates to methods for preparingsingle phase molten baths of alkalinous chlorides, titanium chloridesand alkalinous metals. This is a continuation in part of my application,Serial No. 573,336, filed March 23, 1956, now Patent No. 2,817,631.

In these applications, I have disclosed single phase molten compositionshaving l8% soluble titanium as chloride and .15% alkalinous metaldissolved in molten alkalinous chloride. The average valence of thetitanium being 2.052.7. I have disclosed methods of making thesecompositions, for example, by reaction of sodium reduction with TiCl inthe proportions of TiCl +2Na having a little excess Na to produce aproduct which is dissolved in molten alkalinous chloride to provide thecomposition of my invention.

It should be understood that the definition of the composition of myinvention is based upon analytical methods described in several of myapplications and published in a paper entitled The Chemistry of theReduction of Titanium Chloride in Fused Alkalinous Chlorides bySolutions of Alkalinous Metals, published February 8, 1957, asContributions to Titanium Metallurgy, No. 3, Chicago DevelopmentCorporation, Riverdale, Maryland, February 8, 1957.

The present invention relates to methods of adjusting the averagevalence and alkalinous metal content of the single phase moltensolutions of my invention. It relates especially to the adjustment ofvalence and alkalinous metal content in such solutions by electrolyticmeans.

I have found that when single phase compositions of my invention, inwhich the titanium has an average valence of more than a certainmagnitude related to the titanium content, the average valence may bereduced to that magnitude and a corresponding alkalinous metal contentby making the single phase composition an electrolyte in a cell having atitanium anode and an inert cathode and passing a current at very lowcurrent density on the electrodes.

The following table shows the relationship of average valence to solubletitanium content and dissolved alkalinous metal for a sodium chlorideelectrolyte.

For other electrolytes e.g. 65 SrCl -35% NaCl, the relationship isdifferent. In this electrolyte, the titanium concentrations andalkalinous metal concentrations are higher for a given valence. Apreferred electrolyte of this composition is 8% soluble Ti, 5%alkalinous metal for an average valence of 2.4. Dilution as with theNaCl electrolyte lowers the valence and alkalinous metal content.

It is characteristic of these systems that they may be supersaturatedwith alkalinous metal (alkali and alkaline earth metals) and thattitanium will then crystallize therefrom. My present invention thereforeis limited to those conditions of electrolysis Where supersaturationdoes not take place. The criterion for this is current density, moreespecially cathode current density. I have found that the cathodecurrent density in the process of my present invention should not exceed50 amperes per square foot. Anode current density is substantiallylower.

Another valuable criterion for insuring that the average valence of thetitanium in the bath is lowered without substantial formation of metalis the instantaneous open circuit voltage of the cell. At the start ofelectrolysis, according to my invention, the open circuit voltage Willbe in reverse to the applied voltage. In my invention, I continueelectrolysis until the open circuit becomes a few millivolts in the samedirection as the applied voltage. Electrolysis is carried on beyond thisonly to permit the bath to become uniform by diifusion which isindicated by a steady open circuit voltage of about 20 millivolts in thesame direction as the applied voltage.

The cell for carrying out the electrolyses of my invention is notcritical so long as an inert atmosphere is provided and means forpassing a current from a large surface anode to a large surface cathode.A simple and satisfactory cell is shown in the figure. In this figure,the steel cell (a) serves also as cathode, the anode (b) is a steelbasket containing particulate titanium, e.g. sponge particles. Theconnections to anode and cathode are indicated by the conventionalsymbols; (0) and (d) are argon inlet and outlet respectively to providean inert atmosphere.

Having now described my invention in its general form, I will nowillustrate it by examples.

Example I I react TiCl with Na by adding them to a reactor in smallincrements in the proportions of TiCl +2.2 Na and maintaining atemperature of 600 C. during the reaction. I add this reaction productto molten NaCl at 850 C. in a cell like that of the figure to obtain atitanium concentration of 5.0% soluble titanium having an averagevalence of 2.7. I pass a current through the cell at 10 amperes persquare foot on the cell surface. The initial instantaneous open circuitis mv. in a direction reverse to the applied voltage. I continue thecurrent for 10 hours after which the instantaneous open circuit voltageof the cell has become substantially zero. Further electrolyses for 4hours at 5 amperes brings the instantaneous open circuit voltage of thecell to a steady value of 20 mv. in the direction of the appliedvoltage.

The bath is now a single phase liquid analyzing 5.4% soluble Ti, averagevalence 2.52, alkalinous metal 1.2% by weight.

Example 11 I proceed as in Example I to obtain the reaction product ofTiCl +2.2 Na. I add this to a molten bath of 65% SrCl 35% NaCl at 650C., to produce a single phase melt containing 8% soluble Ti, averagevalence 2.85.

I subject this bath to electrolysis as in Example I except that toobtain zero instantaneous open circuit voltage, I pass 10 amperes for 24hours. I then pass 5 amperes for 4 hours to obtain a steady positivevoltage of 10 mv.

The single phase liquid so obtained analyzes 9% soluble titanium,average valence 2.4, 5% dissolved alkalinous metal.

Example 111 I take TiCl and add enough of this material to molten NaClto provide 1% soluble Ti. The average valence of the melt is 3.0; Ielectrolyze as in Example I for 20 Hours until the instantaneous opencircuit voltage is zero. The resulting bath analyzed 1.45% titanium,average valence 2.05, dissolved sodium .09% by weight.

What is claimed is:

In a process for preparing a single phase molten bath for use as anelectrolyte in a process for electrorefining titanium characterized bypassing a direct current from crudetitanium anode to an inert cathode inan electrolyte of at least one alkalinous chloride containing 1-8%soluble titanium as chlorides, 0.1-5 dissolved alkalinous metal, thetitanium having an average valence from 2.05-2.4, the improvement whichconsists in establishing the optimum relationship of soluble titanium,dissolved alkalinous metal and average eifective titanium valence fortitanium refining by treating a bath of at least one molten alkalinouschloride containing 1-8%"Ti as lower titanium chlorides with an averagevalence of 2.7-3.0 by passing a direct current from a large-surfacetitanium anode to an inert cathode at a cathode current density notexceeding 50 amperes per square foot and a substantially lower anodecurrent density untiltthe instantaneous open circuit voltage initiallyin reverse to the applied voltage is in the same direction as theapplied voltage by a steady value not exceeding 20 millivolts whereby tomaintain the cathode in its initial condition.

